2 Answers
2

In casual spoken English, you could say either one. #1 is a straightforward question while #2 is more of an expression of disbelief or confusion, and it would usually be repeating something observed (or said by someone else).

Consider this short play:

KLARA walks down the street in Copenhagen headed to the pub to meet some friends. Outside the pub she sees a torn-off piece of newspaper with the partial headline "AMERICANS INVADE DANISH--". The rest is torn off.

KLARA rushes into the pub and shows the headline to her friends.

KLARA: What is happening? Did the Americans invade our country or something?

ERIK produces a copy of the newspaper with the whole headline: "AMERICANS INVADE DANISH MUSIC UNDERGROUND". EVERYONE laughs.

Later, KLARA is telling the story to OTHER FRIENDS who have since arrived. HANS is distracted and only half listening.

KLARA: ...so I was walking down the street, and I saw this newspaper that said the Americans had invaded our country, and I--
HANS [interrupting]: Wait, what? The Americans invaded our country?! What's happening?

When you end the sentence with rising intonation, you turn it into a question. And when you write a sentence like this, you indicate the rising intonation by using a question mark ? instead of the usual period . at the end.

I like eggs. ← Statement
I like eggs? ← Question

Making questions in this manner is markedly informal, however. You should avoid doing so in formal situations, including formal essays and on tests. But it's perfectly appropriate in conversations and in online chat, for example.